During the last year we have obtained antibodies against basement membrane components. We now have antibodies against whole basement membrane, pepsin-solubilized-basement membrane-collagen, and collagen-free-basement membrane-glycoprotein. These antibodies will be used in electron microscopic immunohistochemistry to determine the intracellular localization of the different components and to determine cross-reactivity between different basement membranes. The second project concerns the synthesis of basement membrane. This problem is being studied with electron microscopy radioautography, in vitro cell-free synthesis and radioimmunoprecipitation of the specific intracellular basement membrane precursors. From the electron microscopic studies, there is no evidence that label passes through the Golgi region before it is secreted. The cell-free synthesis studies indicate that the enzymes required for both the synthesis of the peptide portion and sugar moieties reside in the microsomal fraction. The radioimmunoprecipitation studies indicate that to synthesize basement membrane the cells synthesize at least three different polypeptide chains. Completion of these studies should provide a clear picture of the synthesis and secretion of this complex macromolecule.